In the field of microelectronics, component size has been reduced significantly, resulting in an increase of the complexity involved with testing of the components. When manufacturing semi-conducting devices, hybrid circuitry, substrates for such devices and circuitry, etc., it is preferred that the components be tested to determine if they may be used reliably in the end product. Generally, it is desirable to conduct such testing before the microminiature devices are installed in the components of the end product. Such testing might be desirable, for example, in testing digital watch circuitry and modules, laser trimming, abrasive trimming, etc.
In many cases, it is desirable to test the microminiature device even before a terminal lead has been applied thereto, in view of the cost and difficulty in applying such leads.
Due to the minute size of the components being tested, it is frequently necessary to provide small probes which can be precisely located relative to a workpiece bearing the structure to be tested. Since the structure is usually of extremely small size, it is also often necessary to provide high power microscopes through which an operator can view the relationship of the circuitry being tested and the tip of the probe.
In many instances, the workpiece upon which the particular object to be tested is mounted also contains several other similar objects, such as various microcircuits, which are to be tested simultaneously. For example, the workpiece might be a ceramic substrate which may have been subjected to baking or heating during its production. In such a case, the substrate is often slightly warped or, at least, not perfectly flat. Obviously, each ceramic substrate will not be warped or disfigured identically to every other substrate. Consequently, some means must be provided to allow each probe tip to come into contact with the object being tested without damaging the probe, the object, or the substrate. For example, in some instances it may be that the object being tested will, upon successful completion of the test, have a lead wire bonded thereto. In many cases, it is required that the lead wire be bonded to virgin, or relatively unscratched material on the device since a junction will not form at a scratched or abraded location on the surface.
Thus, it is desirable to minimize the amount of scratching, commonly referred to as "scrubbing," which takes place between the probe tip and the object being tested. On the other hand, it is often desirable not to totally eliminate such scrubbing since it may be that the face of the object being tested is oxidized; it is necessary for the probe tip to get through the oxide in order to conduct the test properly.
In other words, some scrubbing is desirable, but it is preferable that the scrubbing be confined to a very small area so as to minimize damage to the surface of the object.
As suggested previously, it is often probable that the circuitry on a substrate will be at slightly different levels, relative to a common plane, due to warpage or other phenomena. In other words, some of the circuitry on a substrate will be at a higher elevation than other circuitry. In order that the lowest circuitry may come into suitable contact and be sufficiently scrubbed by its associated probe, it is necessary that provision be made for some amount of overtravel between the highest circuitry pad or object and its associated probe. While this is necessary, it is also imperative that the probes associated with the more elevated circuitry pads neither damage those circuits nor be damaged themselves during testing.
In the prior art, it has been known to provide probes for such testing and various techniques have been employed in an attempt to minimize the relative motion between the probe tip and the pad for the circuitry being tested. With all of these devices, however, it has been necessary for the operator to align the probe tip near one edge of the pad just before contact therebetween so that relative movement between them will cause the tips to scrub across at least a portion of the pad to achieve the desired contact for testing. With all of these prior art devices, the scrubbing takes place in varying degrees, dependent upon the relative elevation of the pads, across a substantially large surface area. For example, if the width of the pad is 6 mils, the scrubbing might occur across anywhere from 10% to 90% thereof. Thus, the possibility of applying a lead or other device to the pad may be substantially reduced. Further, with the prior art devices, the force exerted between the probe tip and the pad has been directly proportional to the distance they move relative to one another after initial contact. In other words, those pads which are most elevated relative to the substrate are subjected to a greater probe tip pressure than those further away.
As can be seen from the above discussion of the prior art deficiencies, it is desirable to provide a probe tip which will sufficiently scrub the surface of a device to be tested so that the oxide layer may be penetrated, without scrubbing so much of the surface that the possibility of attaching a lead thereto or performing other work thereon is significantly reduced.